The present invention relates to novel compositions of polyarylalkane oligomers, and the process for manufacturing them.
These compositions of polyarylalkane oligomers consist of the mixture of two oligomers A and B. Oligomer A is a mixture of isomers of formula: ##STR3## with n1 and n2=0, 1 and 2, given that n1+n2 .ltoreq.3; and oligomer B is a mixture of isomers of formula: ##STR4## with n'1, n"1 and n4=0, 1 and 2, n'2, n"2, n3, n'3 and n5=0 and 1, given that n'1+n"1+n'2+n"2+n3+n'3+n4+n5.ltoreq.2.
This mixture of polyarylalkane oligomers, composed on the one hand of benzyltoluene, dibenzyltoluene and higher homologues, and on the other hand of ditolylphenylmethane and higher homologues, can have the same applications and advantages as monobenzyltoluenes but without possessing their drawbacks. For example, pure monobenzyltoluene is useful as a dielectric for condensers, but has the drawback of crystallizing at -20.degree. C. after supercooling which can be of long duration, which makes it unusable in cold countries. In the same application, dibenzyltoluene does not have this drawback, but its viscosity at low temperatures remains too great to make it usable. The oligomer compositions according to the invention not only have a viscosity which is always compatible with the application envisaged, but moreover they are obtained without sophisticated manufacturing processes or separation processes followed by recombination.
The disadvantages of mono- and dibenzyltoluene have been known for a long time, and numerous replacement mixtures have been proposed starting from polyarylalkane oligomers. Presently, however, it has been difficult to reconcile the quality of the properties of the oligomer products obtained with a commercially feasible method of manufacture.
Thus, in the German Offenlegungsschrift No. 3,127,905, a synthesis process is described which involves the condensation between formaldehyde and aromatic compounds, but this reaction has a poor yield by weight and leads to secondary reactions in the case of the oligomers. In fact, four starting materials are used, namely benzene, toluene, formaldehyde, and sulphuric acid. Besides oligomers of type A, formed by reaction of benzene, toluene and formaldehyde, oligomers of the diphenylmethane type are formed by reaction of benzene and formaldehyde, and of the ditolylmethane type by reaction of toluene and formaldehyde.
Finally, in Japanese Pat. No. 55-5689, the use of the following isomers as dielectric fluids is mentioned:
2,4-dibenzyltoluene PA1 2,6-dibenzyltoluene PA1 o-benzyltoluene PA1 p-benzyltoluene PA1 n1+n2=0, between 56 and 90%, PA1 n1+n2=1, between 7 and 28%, PA1 n1+n2=2, between 1.5 and 8%, PA1 n1+n2=3, between 0.1 and 1%. PA1 n'1+n"1+n'2+n"2+n3+n'3+n4+n5=0 between 1.1 and 5%, PA1 n'1+n"1+n'2+n"2+n'3+n4+n5=1 between 0.25 and 1.5%, PA1 n'1+n"1+n'2+n"2+n3+n'3+n4+n5=2 between 0.05 and 0.5%.
either separately or mixed. Apart from the fact that the synthesis of these isomers requires specific reactions, for example p-benzyltoluene starting from p-methylbenzyl chloride and benzene, or costly separations, it is still necessary subsequently to mix these isomers, which is economically disadvantageous.
Further, the use of benzyl chloride as a starting material for condensation, and its storage present some drawbacks on account of the high reactivity of benzyl chloride, which also explains its high price in comparison with other chlorinated aromatic derivatives.
Thus, products presently sought for dielectric applications, such as monobenzyltoluene or dibenzyltoluene, have only been successfully obtained utilizing syntheses of low selectivity.